1. Field of the Invention
This invention relates to tinted contact lenses and more particularly to a process for tinting contact lenses using reactive dyes.
2. Description of the Prior Art
Contact lenses are frequently tinted or colored for cosmetic or protective purposes. For example, tinted contact lenses may be worn to change or modify the natural color of the iris, or an ultraviolet absorbing lens may be worn after cataract removal to compensate for the loss of the ultraviolet absorption provided by the crystalline lens and thus keep ultraviolet light from reaching the interior of the eye.
It is conventional to color contact lenses by incorporating dyes or pigments, and a number of methods have been disclosed for producing tinted contact lenses containing dyes or pigments. However, many of the methods useful for coloring contact lenses cannot be readily applied to hydrophilic contact lenses. Methods wherein a dye or pigment is merely dispersed within the body of the lens, for example by polymerizing a monomer mixture containing the dye or pigment, are generally unsuitable for coloring hydrophilic contact lenses because the presence of large amounts of water in the highly swollen hydrophilic contact lenses tends to induce migration of the coloring materials. This may occur especially when the lenses are sterilized by boiling in aqueous solution, but may occur even in the aqueous environment of the eye. The disadvantages of such migration are evident, since the lens may fade with the passage of time or the eye may be exposed to coloring materials leached from the lens by the tears. Furthermore, since hydrophilic contact lenses are usually larger in diameter than the cornea, it is conventional to color only the central portion of the lens, so that the color does not appear against the white background of the sclera. In this case, migration of the colorant from the central colored portion to the peripheral colorless portion may produce a cosmetically unacceptable lens.
Examples of lenses made from a material colored by incorporating a solvent (monomer) soluble dye or dispersion of a dye or pigment have been prevalent in the hard contact lens field for many years. In the area of soft hydrophilic lenses this method has been attempted in several instances. Such patents as U.S. Pat. No. 4,252,421 and International Patent Application WO 83/03480 disclose incorporating preformed segments of material previously colored with dyes or pigments into a blank of a hydrophilic polymer suitable for fabricating lenses. U.S. Pat. No. 3,679,504 and British Pat. Nos. 1,163,617 and 1,237,629 teach methods of encapsulating pigments or dyes between polymerised layers of hydrogel materials.
More recently efforts have been made to impart a color to a hydrophilic soft left material in its final water swollen state. This has the advantage that a lens may be tinted as required and obviates the need for maintaining extensive inventories of different types of colored lenses.
A number of known methods for coloring contact lenses rely merely on the dispersion of a dye or pigment in a more or less insoluble form within the lens.
Thus, Newcomer et al., American Journal of Optometry and Physiological Optics 54, 160-164 (1977) disclose the use of adsorbed water-soluble dyes to color hydrophilic contact lenses.
Wichterle, U.S. Pat. No. 3,476,499, discloses coloring a hydrophilic contact lens by diffusing into the lens aqueous solutions of inorganic salts which react within the lens to form an insoluble precipitate.
British Patent 1,547,525, discloses coloring a hydrophilic contact lens by impregnating the lens with an aqueous solution of a color coupler, followed by reaction of the color coupler with a suitable diazonium salt to produce an insoluble azo dye within the lens.
European Patent Application 82026 discloses coloring a hydrophobic contact lens by swelling the lens with a suitable solvent, impregnating the swollen lens with a dye, and removing the swelling solvent from the lens.
British Patent 1,583,492, discloses coloring a hydrophilic contact lens by impregnating with an aqueous solution of the leuco form of a vat dye, then converting the dye to a colored insoluble form within the lens.
All these techniques which result in a colorant dispersed in insoluble form within the lens are subject to the problems of migration and leaching of the colorant either during wear or during the sterilizing process.
Accordingly, attempts have been made to insolubilize a colorant within a contact lens by covalent bonding to the polymer backbone.
Tanaka, U.S. Pat. No. 4,157,892, Japanese Published Unexamined Patent Application 74/113,846, and Japanese Unexamined Patent Application 74/80,190 disclose processes wherein a color coupler covalently bonded to a polymerizable monomer is copolymerized with the structural monomers of the contact lens, and the coupler is subsequently reacted with a dye-forming reagent.
Erickson, U.S. Pat. No. 4,093,361, and British Patent 1,400,892 disclose processes wherein a vinyl comonomer having a covalently bonded dye is copolymerized with the structural monomers of the lens to provide a lens having a dye covalently bonded to the polymer backbone.
Hydrophilic contact lenses of the copolymerized dye or coupler type can suffer from incomplete reaction of the monomer, which results in a lens wherein the monomer colorant may be leached from the lens, with the undesirable consequences of fading, migration and/or eye irritation.
British Patent Application 2,105,061 discloses a method of tinting contact lenses wherein a reactive dye, e.g. a vinyl sulfone dye, is contacted with the contact lens under conditions wherein the dye reacts with the hydroxyl groups of the hydrophilic monomer. While the use of reactive dyes is an effective means of coloring hydrophilic contact lenses, the process disclosed in British Patent Application 2,105,061 does not disclose coloring contact lenses incorporating a substantial amount of N-vinylpyrrolidone monomer. Furthermore the treatment conditions for reacting the dye with the lens involve exposure of the lens to relatively severe conditions such as contact with relatively strong acids and bases.
Hence a need has continued to exist for a simple process for tinting hydrophilic soft contact lenses made from copolymers which include a substantial proportion of N-vinylpyrrolidone in the copolymer and for tinting such lenses under mild conditions.